1. Field of the Invention
This invention relates to a novel polyvinyl alcohol type resin, a monolayer film which comprises this resin, and a laminate that comprises at least one layer comprising this resin.
2. Description of the Related Art
In order to prevent deterioration or putrefaction of food, chemicals and the like caused by oxygen and the like in the air, gas barrier property (particularly oxygen barrier property) are required for their packaging material. Though polyvinyl alcohol resin (to be referred also to as PVA hereinafter) which has excellent gas barrier property, transparency, scent keeping property and the like is used as such a packaging material, being soluble in water, gas barrier property of PVA is insufficient as a packaging material for moist products (e.g., see Non-patent Reference 1).
An ethylene-vinyl alcohol copolymer (to be referred also to as EVOH hereinafter) prepared by copolymerizing PVA with ethylene is also used for the purpose of improving water resistance, but it cannot be said that an EVOH single film is sufficient as a packaging material because its gas barrier property is reduced under a high humidity condition (e.g., see Non-patent Reference 2).
In order to keep gas barrier property at a high level even under a high humidity condition, a laminate in which both sides of an EVOH film are laminated with a water-resistant resin or the like has been put into practical use, but this material is economically disadvantageous because not only the materials are increased but also labor for the laminating treatment is increased.
[Non-patent Reference 1] K. Toyoshima, “Polyvinyl Alcohol” Ed. by C. A. Finch, John Wiley & Sons, 1973, 339
[Non-patent Reference 2] T. Iwanami and Y. Hirai, “Tappi J.”, 1983, 66(10), 85